I stumbled upon this while trying out the java program KD Player.
One of KD Player's main features that attracted me was its customizable 10 band equalizer. Sadly, the player cannot be run in the background which kind of kills the point. I did notice one thing though, when you have set a custom equalizer on, the setting is applied to the phone, not just the application. This means you can set your own EQ, minimize KD Player, and it would still apply to the native music app.
The best part? You dont even need KD Player open. You can set it and quit the application completely, and the equalizer will be set on until you reboot the phone. If you want quick access to turn it on or off or change it, you can simply run it in the background. The EQ is a very handy feature I have been using for a while, you should check it out if you think the phone volume is too low for music or if you just want to enhance your music to your favorite EQ setting.
It can easily give the phone a huge volume boost. Here's my EQ setting, it offers a very very drastic increase in volume (especially through headphones) and still theres no distortion:

One thing to note, the phone for some reason ignores the first two bands, as they dont affect the sound at all and when the preset is saved they revert to 0 by themselves. Only bands 3 through 10 are used.
Simply download KD Player here:
http://www.samsung-impression.org/index.php?topic=1332.msg9023#msg9023Run it, turn on the EQ, and your good to go 8-)